Computer networks have become ubiquitous. Computer networks include the Internet, Service Provider (SP) networks, private networks, and Local Area Networks (LANs). A network such as an SP network may include peripherally located Provider Edge (PE) routers, each of which couples to one or multiple Customer Edge (CE) routers. The PE routers are used to maintain routing and forwarding context for each customer. The CE routers may couple to private LANs associated with one or multiple customers. The private LANs are also referred to as core networks. The CE site can be a MAN or WAN as well. The PE routers learn local customer routes from the CE routers and distribute remote customer routes to the CE router. The PEs use Border Gateway Protocol (BGP) to distribute customer routes to each other. To support operation, the PE routers typically maintain Virtual Routing and Forwarding (VRF) information in a table (a VRF table) dictating how to route and forward traffic through the shared physical network to support corresponding Virtual Private Networks (VPNs) for the different customers. For the core network, an ingress PE uses BGP functions to determine the egress PE. For example, the ingress PE puts the packet in a two-level Multi Protocol Label Switching (MPLS) stack. The top label is used to tunnel packets to the egress PE to accomplish MPLS forwarding through the core network. The bottom label is used by the egress PE to identify either the outgoing FIB rewrite adjacency or VRF table for another lookup. Alternately, an IP VPN may be used wherein PE to PE data is encapsulated in an IP header (e.g., IP, GRE, and L2TPv3)
VPNs provide a secured means for transmitting and receiving data between network nodes even though a corresponding physical network supporting propagation of the data is shared by many users. Typically, the data transmitted between such network nodes (e.g., edge nodes of a service provider network) is encrypted to protect against eavesdropping and tampering by unauthorized parties. According to one conventional technique, an SP network may extend beyond PE nodes to CE nodes.
Certain sites on a network may include redundant PE to CE connections. Sites provided in this manner are referred to as dual-homed sites. In this scenario, one of the PE to CE connections is designated as the preferred path and is the primary path used for communication between the PE, CE and the dual-homed site. The redundant path may be used in certain situations.
In the event of a failure of a device or link that is part of a network, network packets are dropped. In order to overcome this, various techniques are used to determine the location of the failure and to adapt the network to work around the failure. For example, after a failure is detected, the LFIB tables of the various routers may need to be modified to point to corresponding VRFs for lookup and switch back to an alternative PE. This working around the failed device or link is referred to as convergence.